Classical stable population theory is essentially a one-sex theory, depending essentially only on female maternity and female mortality schedules, but not on such characteristics for males. Pollak recently has proposed and elaborated models for the analysis of two-sex populations with monogamous mating that provide an equilibrating mechanism that permits marriage patterns and birth rates to adjust to the population's age-sex composition. His work to date establishes some preliminary conditions for uniqueness and dynamic stability and some examples of nonuniqueness and dynamic instability. The proposed research extends this line of inquiry in both theoretical and empirical directions. The theoretical work has as its principal focus the axiomatic development of alternative functional forms for mating rules; a secondary concern is uniqueness of equilibrium and dynamic stability in two-sex population models. The empirical work will implement and test the models using United States and Japanese data from the past three and a half decades, which encompass very different "marriage squeeze" histories. Simulations will explore questions such as: How much of the change in marriage patterns in these two societies is attributable to changes in the age-sex composition of their marriageable populations? What will be the future evolution of marriage if the parameters of the marriage function remain fixed or follow simple time trends? What difference does it make in modelling population processes and projecting populations if one uses a two- sex rather than a one-sex model? How sensitive are such projections to alternative specifications, assumptions and extensions of the two-sex mating rule?